In this section of the book Ching speak about roofing materials, wall flashing, masonry veneer, thermal insulation, ventilation, roof attic ventilation, crawl space ventilation, and whole house ventilation. Roofing materials provide the water- resistant covering for a roof system. They range in form virtually continuous, impervious membranes to overlapping or interlocking pieces of shingles and tiles. Wall flashing is installed to collect any moisture that may penetrate a wall and divert it to the outside through weep holes. Masonry veneer construction consists of a single wythe of masonry serving as a wether barrier and anchored but not bonded to a supporting structural frame. The primary purpose of thermal insulation is to control the flow or transfer of heat through the exterior assemblies of a building and thereby prevent excessive heat loss in cold seasons and heat gain in hot weather. Whole house ventilators are motor- driven fans for pulling stake air from the living areas of a house and exhausting it through attic and roof vents.